Reflection - The Java Programming Language - page 643

this leads to an invocation of the invoke method on the associated De-
bugProxy instance, passing proxyObj as the proxy object, a Method object
representing the method that was invoked, and all the arguments to the
method call. In our example invoke logs the invocation by adding it to its
list of invoked methods and then invokes the method on the underlying
realObj object, which was stored in the obj field.
The (read-only) history of method invocations on the proxy object can
be retrieved from its DebugProxy instance. This is obtained by passing the
proxy to the static Proxy class method getInvocationHandler :
DebugProxy h =
(DebugProxy) Proxy.getInvocationHandler(proxyObj);
List<Method> history = h.getHistory();
If we hadn't used the newProxyInstance shortcut we would have needed
to write the following in ProxyFor :
Class<?> objClass = obj.getClass();
Class<?> proxyClass = Proxy.getProxyClass(
objClass.getClassLoader(),
objClass.getInterfaces());
Constructor ctor = proxyClass.getConstructor(
InvocationHandler.class);
return ctor.newInstance(new DebugProxy(obj));
The invocation handler's invoke method can throw Throwable . However, if
invoke tHRows any exception that the original method could not throw,
the invoker will get an UndeclaredThrowableException that returns the of-
fending exception from its getCause method.
If you invoke getProxyClass twice with the same parameters (the same
class loader and the same interfaces in the same order) you will get
back the same Class object. If the interfaces are in another order or the
class loader is different, you will get back different Class objects. The